Term Deactivation Research Articles

Combustion and Exhaust Emission Improvement in a 3-Cylinder Mpfi Engine Through Downsizing

This research aims to compare the potential and existing conditions of a small-sized spark ignition (SI) engine with a 1.0-liter capacity suitable for cylinder deactivation. The cylinder deactivation strategy is used to solve the issues of inefficient combustion and increased exhaust emission under part loading. Consequently, the possibility of implementing cylinder deactivation in terms of decreased exhaust pollution has been assessed. A computerized, 1.0-liter, 4-stroke, water-cooled, spark-ignition engine with an open engine control unit (ECU) and multi-point fuel injection (MPFI) was used for the trials. Both modes were tested at 2500 revolutions per minute (RPM) under loads of 15, 30, and 45 N-m. The spark plug and fuel injector deactivate the cylinder. The results show that when the highest possible load is used, the peak cylinder pressure is 55.78% higher, and the maximum heat release rate is 53.96% more in the deactivation mode than in the traditional mode. In deactivation mode, the mass fraction consumed is larger at each crank angle point, suggesting a faster rate of combustion and increased combustion efficiency. The increased mean gas temperature permits the catalytic converter to perform more efficiently after downsizing. When compared to the conventional mode, carbon monoxide (CO) emission is almost non-existent at full load, unburned hydrocarbon (UHC) is reduced by 92.89%, and oxides of nitrogen (NOx) are reduced by 35% in the deactivation mode. Furthermore, the experiment indicated that, when employed at part load, the deactivation mode is more beneficial than the standard mode in terms of better combustion stability and lesser emissions.

Desilicated ZSM-5 zeolite: Catalytic performances assessment in methanol to DME dehydration

Abstract The modification of the physicochemical properties of synthetic zeolites is an important element when these materials are applied as heterogeneous catalysts in the view of more sustainable and effective processes. In this work, desilicated ZSM5 samples were tested on the methanol to dimethyl ether dehydration. Desilication time strongly affects the textural and acidic properties of the samples, and those characteristics determined a different catalytic behaviour. Contact time of 60 min with NaOH solution (alkaline desilication) favourably impact on the activity of the catalysts and its stability against deactivation in terms of methanol conversion and yield to DME, in comparison with parent zeolite and sample prepared after 30 min of desilication. This effect is due to a combination of changes in the properties of acidic sites and mesoporous volume, as confirmed by stability test over 80 h of reaction. The analysis of formed coke confirmed this evidence since the most performing catalyst showed the lowest tendency to form coke as the main consequence of the improved accessibility to the acid sites determined by the induced mesoporosity.

An Analysis of Threshold Criteria and Conditions for Variable Speed Limit Deactivation

The study demonstrates the relative effectiveness and trade-offs amongst various threshold conditions for Variable Speed Limits (VSL) deactivation in terms of the control stability and efficiency. Reduced speed limits must be restored when the traffic interruption is resolved in a prompt and safe manner. Most VSLs in practice rely on a threshold-based control, which determines the speed limit adjustment by comparing detector readings to pre-determined threshold conditions. We tested three types of algorithmic parameters including occupancy, average speed, and consistency-check conditions. The test was carried out using the actual detector data, collected from three different segments of Pacific Motorway in Brisbane, Australia. Our analysis revealed that occupancy could be the most effective threshold over average speed. Operational fluctuation of VSL can be significantly reduced by selecting appropriate occupancy threshold values. We also tested four different consistency check conditions including a conditional deactivation approach. This approach makes the deactivation decision conditional upon the traffic status in the immediate downstream segment to avoid flushing upstream traffic into an active or potential bottleneck downstream. The test results and findings of this study may be useful for practitioners and researchers for developing VSL deactivation rules and associated operational strategies.

Partial oxidation of methane over monometallic and bimetallic Ni-, Rh-, Re-based catalysts: Effects of Re addition, co-fed reactants and catalyst support

Partial oxidation reactions of CH4 over monometallic Ni, Rh, Re and bimetallic Re-Ni catalysts supported by Al2O3 were studied at 400–700 °C. Among monometallic catalysts, Rh/Al2O3 exhibited the highest catalytic activity. Lower CH4 conversion and H2 yield were observed over Ni/Al2O3 catalyst, while Re/Al2O3 catalyst did not promote the reaction under the studied condition. Addition of Re over Ni to form a bimetallic catalyst considerably promoted the activity of Ni/Al2O3 catalyst, particularly at a higher temperature (600 °C). Re-Ni proportion was then optimized; Re-Ni/Al2O3 at Re:Ni ratio of 3:7 resulted in a significantly higher CH4 conversion as well as H2 and CO yields when compared to noble-metal Rh/Al2O3 catalyst. Stability testing of Re-Ni/Al2O3, Ni/Al2O3 and Rh/Al2O3 catalysts was also conducted. After 18-h operation, Re-Ni/Al2O3 catalyst still exhibited high stability with slight deactivation in terms of H2 yield, whereas Ni/Al2O3 and Rh/Al2O3 catalysts showed higher deactivation rates. Post-reaction temperature programmed oxidation confirmed the better resistance toward carbon deposition of Re-Ni/Al2O3 catalyst. The effect of steam and CO2 addition on the Re-Ni/Al2O3 catalyst performance was also investigated. The presence of a suitable H2O content could increase H2 and CO yields and reduce the amount of carbon deposition, whereas the presence of CO2 showed undesirable influence on the reaction by reducing CH4 conversion and H2/CO ratio. Lastly, Re-Ni/Gd-CeO2 catalyst was prepared and tested to study the effect of catalyst support. The catalyst stability and resistance toward carbon deposition were significantly improved, which could be due to the high oxygen storage capacity of Gd-CeO2.

Role of Pt during hydrodeoxygenation of biomass pyrolysis vapors over Pt/HBEA

1.3wt% Pt/HBEA and HBEA were studied as catalysts for the hydrodeoxygenation of pine pyrolysis vapors at 500°C. Both catalysts showed high initial conversion of oxygenated pyrolysis products into aromatic hydrocarbons, while Pt/HBEA showed higher stability in terms of hydrocarbon productivity and deferred breakthrough of oxygenated compounds. Among 1-, 2- and 3-ring aromatic hydrocarbons, Pt/HBEA had a significantly higher selectivity than HBEA towards unalkylated aromatics (e.g., benzene) as compared to the corresponding alkylated aromatics (e.g., toluene and xylene). Additionally, Pt addition to HBEA decreased coke deposition and improved resistance to pore and acid site blockage as determined by TPO, N2 physisorption, and NH3 TPD. The ability of Pt to promote cleavage and hydrogenation of methoxy and methyl groups was observed by increased methane production over Pt/HBEA relative to HBEA. A progressive decrease in the methane production over Pt/HBEA correlated with deactivation in terms of reduced benzene formation, breakthrough of oxygenated products, and increased formation of polynuclear aromatics and their degree of substitution, which indicate coke formation. The increased methane yield and suppressed coke formation with the addition of Pt is attributed to hydrogen spillover, through which hydrogen activated on Pt can subsequently migrate to the HBEA support to reverse the coke-forming hydrogen abstraction reaction.

Evaluation of refined theories for multilayered shells via Axiomatic/Asymptotic method

This paper is devoted to refined shell theories for the analysis of isotropic and laminated shells. Refined theories are built by assuming higher expansion order for the displacement field in the shell thickness directions. The implementation of these theories is made according to the Carrera unified formulation (CUF) which makes it possible to obtain shell governing equations in terms of fundamental nuclei whose form is independent of the chosen theory shell. Equivalent single layer and layer wise schemes are used. The axiomatic/ asymptotic technique is employed to evaluate the effectiveness of each displacement variable in the adopted displacement expansion. The error introduced by each term deactivation is evaluated with respect to a reference solution and according to a given error criterion; if the error computed does not exceed an a priori defined threshold the term is considered as not relevant and discarded. In this way it is possible to construct reduced models for each stress/displacement component. Attention has been restricted to closed form Navier type solutions and simply supported orthotropic shells are considered in the numerical investigation. Analysis of the displacement variables relevance is performed considering the influence of the kind of material and of the geometry, specifically isotropic and laminated materials and thick and thin shells. “Best”′ reduced models are proposed and related distributions are discussed.

CO2 reforming of methane over Ni-Cu/Al2O3-ZrO2 nanocatalyst : The influence of plasma treatment and process conditions on catalytic properties and performance

Argon glow discharge plasma was applied for treatment of impregnated Ni-Cu/Al2O3-ZrO2 nanocatalyst. The catalytic performance toward CO2 reforming of methane and the physicochemical properties were investigated by means of GC, BET, XRD, FESEM, TEM, EDX, TG-DTG, XPS and FTIR techniques. The plasma-treated nanocatalyst contains smaller crystal size and high dispersion of NiO. Plasma treatment decreased particle size and plasma high energy species flattened particles on support, increasing the interaction between support and active metals which leads to high catalytic activity. Low temperature activity and H2/CO ratio closer to 1 was observed for plasma-treated nanocatalyst compared to non-treated sample. Moreover, higher product yield and H2/CO ratio was found in CH4/CO2=1 rather than CH4/CO2=1.5. Time on stream test during 1,440 min at 850 °C showed plasma-treated Ni-Cu/Al2O3-ZrO2 nanocatalyst did not experience any deactivation in terms of CH4 and CO2 conversion and H2/CO ratio.

Simultaneous estimation of kinetics and catalysts activity during cracking of 1,3,5-tri-isopropyl benzene on FCC catalyst

Catalytic cracking reactions, performed on commercial catalysts, are difficult to follow because of the simultaneous deactivation of the catalyst as consequence of coke deposition on catalyst surfaces during cracking of hydrocarbon molecules. In this work, a model for catalyst deactivation in terms of fouling because of blockage of micropores of the catalyst is used to estimate activity independently of reaction rates; later cracking kinetic rates of a model compound are estimated. It was found that the expected low energy of coke deposition reactions dominate the process, however these reactions are not easy to estimate a priori because of the definition of coke as a lumped entity. A comprehensive model of a CREC-Riser simulator Reactor is developed in order to consider mass balances for each specific operating condition. Three temperatures and two contact times are used to evaluate frequency factors and activation energies of the reactions that take place during the catalytic cracking of 1,3,5-tri-isopropyl benzene in two cases, with catalyst coming from an industrial unit and with catalyst pre-coked in laboratory. A methodology to separate activity and apparent kinetics in this kind of reactions is proposed.

Editorial: Apoptosis is Critical to Pain Control

Dear Readers—Pain frequently involves a neural circuit that can either magnify or suppress pain, depending on the way the brain processes the pain signals and depend- ing on the pain causing or pain suppressing compounds that are secreted in the skin. Pain is essential to life, since it helps us to avoid damaging situations. The most abun- dant pain sensors are in the skin, and are called the tra- nsient receptor potential cation channels (TRP). The TRP family contains many members such as the vanillloid receptors (TRPV), the canonical receptors (TRPC), the ankyrin repeat receptors (TRPA), the polycystin - recaptors (TRPP), the melastatin receptors (TRPM) and the mucolipin receptors (TRPML) [1]. These cation channels allow cations to cross the plasma membrane, such as so- dium andcalcium. In the skin, these recetors are found pon small unmyelinated (C-type) or thinly myelinated (A delta-type) nerve terminals [2]. Their cell bodies are in the dorsal root ganglion with dendrites that form syn- apses in the spinal cord. These synapses are formed with ascending CNS neurons that have cell bodies in the hy- pothalamus, hippocampus and other areas. These CNS neurons form synapses with other CNS descending neu- rons that form synapses in the spinal cord with descend- ing neurons that have nerve terminals in the skin[2]. These descending neurons are neurotrophin secreting neurons. TRP channels are activated by histamine, bradykinin, fatty acid metabolites, endocannabinoids, cannabinoids, ATP, acid, heat, cold, prostaglandins, cytokines, capsai- cin, monoterpenoids and other stimuli. The initial sensa- tion can be heat, cold, pain or itching that can be several minutes in duration. Usually, prolonged activation of the TRP channels, for more than 20 30 minutes or so, r- e- sults in long term deactivation and pain relief. This is how capsaicin and the monoterpenoids, such as menthol, relieve pain [2]. Initial receptor activation is followed by long term deactivation. Arachidonic acid produces pain causing prostaglandins and pain relievingresolvins, in a balance. Resolvins deactivate TRP channels resulting in pain relief [3]. Endocannabinoids, prostaglandins, re- solvins, histamine, bradykinin, cytokines, ATP and other endogenous compounds are produced where they are needed and have short durations of action. This natural pain controlling system can be altered by nonsteroidal anti-inflammatory drugs (NSAIDS) and other drugs, re- sulting in the inability to control pain naturally. This can be disastrous for patients. Pain can be blocked at any point in the neural circuit. Opioids block pain in the brain. NSAIDS block pain in the skin and other sites. Menthol and other monoterp- enoids block pain in the skin, where they are applied. Monoterpenoids are probably safer than opioids and NSAIDS since monoterpenoids are applied in small amounts to the skin. Opioids and NSAIDS are taken orally in large doses and penetrate into many organs of the body. As of 2013, prescription opioids kill 14,000 patients yearly. As of 2009, NSAIDS cause 100,000 ul- cers and 10,000 deaths annually. TRP channels allow calcium to penetrate into nerve terminals. This can activate apoptosis mechanisms that result in nerve terminal destruction [4]. This nerve ter- minal destruction in the skin is a prominent feature of Adams disease, a disease that involves severe pain from over activation of TRP channels by cold and other stim- uli [5]. Adams disease appears to be caused by dysfunc- tional TRP receptors in the skin. Destruction of nerve terminals in the skin may cause long term pain relief. The descending neurons that terminate in the skin se- crete neurotrophins that are essential for the regrowth of TRP containing nerve terminals. The neurotrophin se- creting nerve terminals help reestablish the neural circuit involved in pain sensation.

Hydrogen and syngas production from two-step steam reforming of methane using CeO 2 as oxygen carrier

Abstract CeO 2 oxygen carrier was prepared by precipitation method and tested by two-step steam reforming of methane (SRM). Two-step SRM for hydrogen and syngas generation is investigated in a fixed-bed reactor. Methane is directly converted to syngas at a H 2/CO ratio close to 2:1 at a high temperature (above 750 °C) by the lattice oxygen of CeO 2; methane cracking is found when the reduction degree of CeO 2 was above 5.0% at 850 °C in methane isothermal reaction. CeO 2-δ obtained from methane isothermal reaction can split water to generate CO-free hydrogen and renew its lattice oxygen at 700 °C; simultaneously, deposited carbon is selectively oxidized to CO 2 by steam following the reaction (C+2H 2O→CO 2+2H 2). Slight deactivation in terms of amounts of desired products (syngas and hydrogen) is observed in ten repetitive two-step SRM process due to the carbon deposition on CeO 2 surface as well as sintering of CeO 2.

The influence of carbon laydown on selectivity in the hydrogenation of pentenenitriles over supported-nickel catalysts

Pentenenitriles contain two-reducible functionalities: a carbon–carbon double bond and a nitrile group, either of which may undergo hydrogenation during reaction. In this work we show how the deposition of hydrocarbonaceous material on the catalyst surface during pentenenitrile hydrogenation over 16 wt.% Ni/Al 2O 3 and 10 wt.% Ni/SiO 2 catalysts has a significant impact on the observed catalytic activity and selectivity. The role of carbon laydown in controlling catalytic performance in this system has been evaluated through activity measurements and mechanistic studies employing a Tapered Element Oscillating Microbalance (TEOM) and a conventional flow-through reactor. TEOM data indicating the deposition of carbonaceous material during reaction are correlated with kinetic analysis which provides a description of catalyst deactivation in terms of the deactivation of groups of active sites. Specifically five distinct active sites are shown to exist on Ni/Al 2O 3 including a hydrogenation site on the support, which is not present in the case of Ni/SiO 2. The nature and strength of these sites are discussed. Furthermore, deuteration studies provide mechanistic insights suggesting that the hydrogenation reaction proceeds via a cyclic intermediate. The reported data identify a correlation between mass laydown on specific active sites and deactivation, thereby demonstrating the influence of hydrocarbonaceous deposits on selectivity. Both the location and the nature of such deposits are crucial in determining its influence on reaction.

Autothermal reforming of methane over Rh/Ce 0.5Zr 0.5O 2 catalyst: Effects of the crystal structure of the supports

Autothermal reforming of methane (ATR) was studied over Rh catalysts supported on Ce 0.5Zr 0.5O 2 solid solution, which were synthesized by four different routes, including reverse micro-emulsion (ME), co-precipitation (CP), urea-combustion (UC) and sol–gel (SG) method. The textural and structural properties of the as-prepared solid solutions were carefully examined by means of BET, TEM, XRD and Raman techniques. Results showed that the ME sample exhibited a single cubic phase, whereas tetragonal or mixed phases such as cubic CeO 2-rich and tetragonal ZrO 2-rich phases, were found in the case of CP, UC and SG. Vegard's rule revealed that the homogeneity of these as-prepared solid solutions followed the order of ME > CP > UC > SG. TPR and CO-pulse experiments were adopted to evaluate the reducibility and the oxygen storage capacity (OSC) of the catalysts. It was found that the more homogenous the solid solution is, the more reducibility it is, i.e. both the reducibility and OSC followed the same order as that of homogeneity. Rh/ME showed the highest activity and H 2/CO ratio and such performance was maintained without significant loss during 10 h experiment. On the contrary, the other three catalysts having mixed phases showed remarkably deactivation in terms of H 2/CO due to the loss of BET area. To elucidate the resistance toward carbon formation of these catalysts, methane decomposition experiments and following temperature-programmed-oxidation (TPO) were studied. As expected, the resistance toward carbon formation could be enhanced by the improved OSC of the catalyst.

“Enzyme Test Bench,” a high‐throughput enzyme characterization technique including the long‐term stability

A new high throughput technique for enzyme characterization with specific attention to the long term stability, called "Enzyme Test Bench," is presented. The concept of the Enzyme Test Bench consists of short term enzyme tests in 96-well microtiter plates under partly extreme conditions to predict the enzyme long term stability under moderate conditions. The technique is based on the mathematical modeling of temperature dependent enzyme activation and deactivation. Adapting the temperature profiles in sequential experiments by optimal non-linear experimental design, the long term deactivation effects can be purposefully accelerated and detected within hours. During the experiment the enzyme activity is measured online to estimate the model parameters from the obtained data. Thus, the enzyme activity and long term stability can be calculated as a function of temperature. The engineered instrumentation provides for simultaneous automated assaying by fluorescent measurements, mixing and homogenous temperature control in the range of 10-85 +/- 0.5 degrees C. A universal fluorescent assay for online acquisition of ester hydrolysis reactions by pH-shift is developed and established. The developed instrumentation and assay are applied to characterize two esterases. The results of the characterization, carried out in microtiter plates applying short term experiments of hours, are in good agreement with the results of long term experiments at different temperatures in 1 L stirred tank reactors of a week. Thus, the new technique allows for both: the enzyme screening with regard to the long term stability and the choice of the optimal process temperature regarding such process parameters as turn over number, space time yield or optimal process duration. The comparison of the temperature dependent behavior of both characterized enzymes clearly demonstrates that the frequently applied estimation of long term stability at moderate temperatures by simple activity measurements after exposing the enzymes to elevated temperatures may lead to suboptimal enzyme selection. Thus, temperature dependent enzyme characterization is essential in primary screening to predict its long term behavior.

‘Enzyme Test Bench’: A biochemical application of the multi-rate modeling

In the expanding field of ‘white biotechnology’ enzymes are frequently applied to catalyze the biochemical reaction from a resource material to a valuable product. Evolutionary designed to catalyze the metabolism in any life form, they selectively accelerate complex reactions under physiological conditions. Modern techniques, such as directed evolution, have been developed to satisfy the increasing demand on enzymes. Applying these techniques together with rational protein design, we aim at improving of enzymes' activity, selectivity and stability. To tap the full potential of these techniques, it is essential to combine them with adequate screening methods. Nowadays a great number of high throughput colorimetric and fluorescent enzyme assays are applied to measure the initial enzyme activity with high throughput. However, the prediction of enzyme long term stability within short experiments is still a challenge. A new high throughput technique for enzyme characterization with specific attention to the long term stability, called ‘Enzyme Test Bench’, is presented. The concept of the Enzyme Test Bench consists of short term enzyme tests conducted under partly extreme conditions to predict the enzyme long term stability under moderate conditions. The technique is based on the mathematical modeling of temperature dependent enzyme activation and deactivation. Adapting the temperature profiles in sequential experiments by optimum non-linear experimental design, the long term deactivation effects can be purposefully accelerated and detected within hours. During the experiment the enzyme activity is measured online to estimate the model parameters from the obtained data. Thus, the enzyme activity and long term stability can be calculated as a function of temperature. The results of the characterization, based on micro liter format experiments of hours, are in good agreement with the results of long term experiments in 1L format. Thus, the new technique allows for both: the enzyme screening with regard to the long term stability and the choice of the optimal process temperature. The presented article gives a successful example for the application of multi-rate modeling, experimental design and parameter estimation within biochemical engineering. At the same time, it shows the limitations of the methods at the state of the art and addresses the current problems to the applied mathematics community.

Effects of cognitive demands on postmovement motor cortical deactivation

Postmovement beta-rebounds induced by different intermovement intervals were investigated using magnetoencephalography in 14 healthy participants to test the hypothesis that postmovement motor cortical deactivation over the primary motor cortex depends on movement-related cognitive demands. Shorter latency and lower amplitude in postmovement beta-rebounds over the contralateral primary motor cortex were noted in the short-movement interval movement (repetitive finger lifting). Greater latency span of postmovement beta-rebounds jittering using single-trial analysis in the long-movement interval movement (discrete finger lifting) was observed. The study elucidates that the temporal interval between two adjacent movements reflecting different degrees of cognitive demands can affect postmovement motor cortical deactivation in terms of postmovement beta-rebounds latency and amplitude, and latency span of postmovement beta-rebounds jittering. Postmovement motor cortical deactivation can reflect cognitive demands in addition to motor and somatosensory processing.

Application of a three-dimensional network model to the coke formation in FAU, MFI and BEA zeolites

Three-dimensional site-bond-site network modeling was applied to simulate the deactivation process of three types of zeolites: BEA, FAU and MFI. A simple process rate model was used to describe the deactivation in terms of relative activity while a detailed Monte-Carlo reaction model was used to study the coke formation, including adsorption, desorption, reaction and diffusion effects. The simulation results were compared with experimental data for coke formation. The study shows the importance of catalyst morphology and topology described in the present model by measurable parameters like: connectivity of network and size distribution of cavities and channels. The present model correlates effectively the available experimental deactivation data for the cases studied, both for short or long times of reaction, showing the importance of taking the pore structure into account when modeling catalyst deactivation.

Research and development of dimethyl ether as clean fuel

The modification of the physicochemical properties of synthetic zeolites is an important element when these materials are applied as heterogeneous catalysts in the view of more sustainable and effective processes. In this work, desilicated ZSM5 samples were tested on the methanol to dimethyl ether dehydration. Desilication time strongly affects the textural and acidic properties of the samples, and those characteristics determined a different catalytic behaviour. Contact time of 60 min with NaOH solution (alkaline desilication) favourably impact on the activity of the catalysts and its stability against deactivation in terms of methanol conversion and yield to DME, in comparison with parent zeolite and sample prepared after 30 min of desilication. This effect is due to a combination of changes in the properties of acidic sites and mesoporous volume, as confirmed by stability test over 80 h of reaction. The analysis of formed coke confirmed this evidence since the most performing catalyst showed the lowest tendency to form coke as the main consequence of the improved accessibility to the acid sites determined by the induced mesoporosity.

The gas phase hydrodechlorination of chlorobenzene over nickel/silica

The gas phase hydrodechlorination of chlorobenzene over the temperature range 473 K⩽T⩽573 K has been studied using a 1.5% (w/w) Ni/SiO2 catalyst. Reproducible turnover frequencies are quoted and the effects of varying such process variables as reaction time and temperature, contact time, chlorobenzene and hydrogen partial pressures are presented. The catalyst was 100% selective in promoting hydrodechlorination and the aromatic ring remained intact in every instance. Under reaction conditions far removed from equilibrium conversions, the catalyst exhibited no appreciable short term deactivation while the maintenance of long term activity was also established. Chlorine coverage of the catalyst surface under reaction conditions was probed indirectly by monitoring, via pH changes in an aqueous NaOH trap, HCl desorption after completion of the catalytic step. The hydrogenolysis of bromobenzene, 2-chlorophenol and 3-chlorotoluene under the same reaction conditions were considered for comparative purposes where the turnover frequencies decrease (at 573 K) in the order 2-chlorophenol>3-chlorotoluene>chlorobenzene>bromobenzene; reactivity is discussed in terms of thermodynamic limitations and reactant/catalyst interactions. Reaction orders with respect to hydrogen and chlorobenzene partial pressures were obtained at different reaction temperatures and the experimental rate data are adequately represented by an extended power rate expression that approximates the Langmuir–Hinshelwood model for non-competitive adsorption. © 1999 Society of Chemical Industry

Gas phase catalytic hydrodechlorination of chlorophenols using a supported nickel catalyst

The gas phase hydrodechlorination of single component and mixtures of o-, m- and p-chlorophenol was studied over the temperature range 423 K≤ T≤573 K using a 1.5% (w/w) Ni/SiO 2 catalyst. The variation of catalyst activity with time-on-stream for each isomer is illustrated and the role of reaction temperature and thermodynamic limitations are addressed. The catalyst exhibits both short term and irreversible long term deactivation which is accounted for in terms of competitive adsorption and electronic effects. The hydrogen treatment of both phenol and chlorobenzene under the same reaction conditions are also considered for comparative purposes. The presence of the hydroxyl function enhances the rate of hydrodechlorination via an inductive effect. The relationship between rate and isomer structure is discussed on the basis of reactant adsorption where steric hindrance, in the case of the ortho-form, appreciably restricts dechlorination to such an extent that o-chlorophenol remains unreacted in equimolar o-/ p- and o-/ m-chlorophenol mixtures. Catalytic hydrodechlorination is viewed as a non-destructive low energy methodology for handling concentrated chlorine gas streams and relationships that describe the dependence of dechlorination rate on chlorine concentration are provided and can be used to evaluate the productive lifetime of the catalyst.

Role of hydrogen in catalytic dehydrogenation: Film diffusion controlled deactivation

The function of hydrogen used as carrier gas in catalytic dehydrogenation is to increase the selectivity and stability of catalysts. It slows down catalyst deactivation by either inhibiting deposition of potential coke precursors or facilitating their desorption by rehydrogenation. This function, in gas-solid catalytic dehydrogenation appears to be interphase mass transfer controlled by increased hydrogen linear flow velocities decreasing the extent of deactivation. Besides, deactivation appears to progress through two regimes, an initial short term followed by a long term deactivation.